Nuclear Factor (NF)-kB signaling is important for the maintenance of intestinal immune homeostasis. Inappropriate NF-kB activity results in inflammatory bowel disease (IBD) and thus must be tightly regulated. The ubiquitin-modifying protein A20 (also known as TNFa induced protein 3, TNFAIP3) is a critical regulator of NF-kB signaling as demonstrated by A20-deficient mice which develop spontaneous intestinal inflammation and die perinatally due to spontaneous systemic inflammation and cachexia. Recent genetic studies have identified TNFAIP3 as a candidate gene associated with inflammatory bowel disease. Therefore, an understanding of how A20 regulates intestinal immune homeostasis will be critical in understanding the pathogenesis of IBD and the development of novel therapeutics for patients with IBD. A20 is a unique ubiquitin-modifying enzyme with both deubiquitinating and ubiquitin ligase activity. Preliminary data suggests that A20 is critical in restricting TNF, TLR and NOD signaling and preventing in spontaneous intestinal inflammation and IBD. The proposed research has three specific aims: 1) characterize and define how the A20 ubiquitin modifying domains restrict tumor necrosis factor (TNF) signaling, 2) characterize and define how the A20 ubiquitin modifying domains restrict toll-like receptor (TLR) signaling, and 3) determine how the A20 ubiquitin modifying domains are involved in restricting the development of inflammatory bowel disease in mouse models. These studies will provide mechanistic insight into how A20 restricts inflammatory signaling cascades and regulates intestinal immune homeostasis. These studies will provide potential new leads for the development of novel therapeutics for IBD. The proposed studies will be undertaken with the mentorship of Dr. Averil Ma. A Career Development Plan including didactic courses, research seminars and presentations, and journal clubs has been developed along with a proposed research publication and career timeline. A career development committee of internationally recognized mentors, collaborators, and advisors with expertise in the fields of IBD, immunology, human genetics and apoptosis biology will help ensure that Dr. Lu meets the proposed milestones. The proposed studies will establish a firm foundation for an R01 grant and allow Dr. Lu to become an independent investigator in mucosal immunology and IBD.